In a mobile communications network, functions called Network Management System (NMS) or Operations Support System (OSS) are responsible for performance management. Performance is usually measured on the basis of a performance metric, such as Key Performance Indicators (KPIs). The NMS/OSS measures, collects and analyzes KPIs in the network. KPI changes may indicate performance degradation.
When performance degradation occurs, it is necessary for the operator to find out the main cause of the problem (root cause analysis) in order to be able to initiate an appropriate action. Similarly, when the operator would like to increase the level of service provided to its customers, the operator needs to determine the main bottlenecks for achieving higher performance levels and invest in removing those main bottlenecks.
Performance and service quality in mobile communications networks are influenced by a large number of parameters. For example, throughput is influenced by the radio channel quality of a given user terminal but also depends on the number of other active user terminals in the cell, the traffic of those user terminals, Internet side bandwidth, delays and server limitations, just to name a few.
Similarly, a performance degradation seen in the mobile communications network may have a number of reasons. In some cases low performance can immediately be connected to severe network incidents (e.g., cell outage) visible directly from a fault management system. In other cases, however, the decrease in performance cannot be easily explained. For example, there may be no direct connection to any severe network problems or incidents. In particular, there are many parameters in the network that can have direct or indirect impact on performance. These parameters might depend on each other. Thus, usually it is not trivial to find the cause of the performance problems due to the multivariate dependence of the performance on the parameters and the complicated inter-dependence between the parameters.
Any analytical model that targets at characterizing the dependency of a performance metric on individual parameters in a mathematical way based on theoretical knowledge inherently suffers from inaccuracy (i.e., not matching with situations in real networks) and incompleteness (i.e., can take into account only a limited set of parameters). As another example, there is often a complex inter-dependency between the parameters (parameter inter-dependency problem). In other cases, there may be insufficient number of measurements in the network equipment to investigate. Also, different parameters have different units that cannot be properly combined. Still further, numeric and nominal parameters need to be handled in the same framework, which is not a trivial task.
Consequently, in order for a network operator to understand the bottleneck parameters that limit a desired level of a given performance metric (e.g., throughput) in the network, or to identify the root cause of a problem, there is need for mechanisms that can automatically derive this information without relying on any analytical and theoretical modeling.
Several solutions for the problem of root cause analysis in mobile communications networks have been proposed. WO 2013/044974 A1 teaches a root cause analysis technique for performance management according to which performance measurements are associated with identifiers, and the network topology is linked with the measurements through the identifiers. WO 2011/045736 A1 teaches a root cause analysis technique in which it is quantified (based on measurements for each parameter) how much a parameter influences the performance. The quantification includes a factor scoring system and database, which has the advantage of having the same unit for all parameters.
Document EP 2 584 814 A1 may be construed to disclose a method for tracking an International Mobile Equipment Identity (IMEI) of User Equipment (UE), which includes: obtaining, by a Radio Network Controller (RNC), an IMEI of UE from an identity response message, which is sent by the UE to respond a non-access stratum identity request message, after success of signalling connection of a UE call when the RNC establishes Radio Resource Control (RRC) connection with the UE; and saving, by the RNC, the obtained IMEI in a user log generated in a process of the UE call. It is further disclosed an RNC for tracking an IMEI of UE.
Document WO 2011/076253 A1 may be construed to disclose a method by which a network element in a telecommunications network can report factors that have limited the performance of a UE in an observation period. A bottleneck score is calculated for each factor, the bottleneck score providing a measurement of the extent to which that factor has limited the performance of that UE compared to other factors in the observation period. A data record for the UE is populated with the bottleneck scores and sent in a report towards upper layer management functions. When these reports are received (e.g. by a MME) they may be complemented with global entities of the users and aggregated measures created. The bottleneck scores may be calculated by collecting per-UE performance counters from a radio scheduler and estimating an actual UE performance from the collected performance counters, replacing one or more of the measured performance counters with a hypothetical value reflecting a particular factor operating ideally, and estimating a theoretical user performance based on the hypothetical value and remaining performance counters, and assigning a bottleneck score for that factor by comparing the estimated actual user performance with the estimated theoretical user performance.